MAC Preview has automatically added password to 3 x pdf's

I have noticed others posting this same complaint about Preview locking PDFs, yet cannot reproduce any password-locked PDF simply by annotation and then saving it. Not on any version of Monterey through v12.6 nor Big Sur through 11.7 — Intel or Apple Silicon. Where are these PDFs being saved too?

I have opened, annotated, and manually saved PDFs to my local drive that were originally created with the following:

1. MacTex's XeTex
2. Groff output via Apple's pstopdf(1) utility
3. LibreOffice Writer 7.4.2 as PDF/A-3B/UA-1
4. Apple's PDFContext from Pages v12.1
5. By opening and exporting an existing PDF from Affinity Designer 1.10.5 as a PDF/X-3 document.
6. PDF created by InDesign 17.1 (Windows) using Adobe PDF Library 16.0.5

None of this variety of PDFs exhibited any locks on the PDF after a manual save from Preview.

You mean all of a sudden, the pdf is password protected, as in when you double-click to open it shows this:

I have no idea how this would happen from pressing Command-S to save a document.

Very troubling, indeed.

The only thing I can think of right now is to use Time Machine to recover an earlier version of the file before it became password protected.